Key Facts
The RBMK design used at Chernobyl has a "positive void coefficient." This means the nuclear chain reaction and power output increases when cooling water is lost. The large value of the "positive void coefficient" caused the uncontrollable power surge that led to Chernobyl's destruction. To make matters worse, the Soviet operators had disengaged several safety and cooling systems and taken other unauthorized actions during a test of electrical equipment. This made the Chernobyl unit even more vulnerable to the uncontrollable power surge. The power surge and chemical explosions that followed were so powerful that they lifted the 1,000-metric-ton cover off the top of the reactor.
The Chernobyl plant did not have the massive containment structure common to most nuclear power plants elsewhere in the world. Without this protection, radioactive material escaped to the environment. However, because the estimated energy released by the explosions was greater than most containment designs could withstand, it is highly unlikely that a containment structure could have prevented the release of radioactive material at Chernobyl. The crippled Chernobyl reactor is now enclosed in a hurriedly constructed concrete sarcophagus, which is growing weaker over time. The Ukrainian government is considering the feasibility of building a second structure over the sarcophagus.
Soviet scientists have reported that the Chernobyl Unit 4 reactor contained about 190 metric tons of uranium dioxide fuel and fission products. Estimates of the amount of this material that escaped range from 13 percent to 30 percent.
Contamination from the Chernobyl accident was not evenly spread across the surrounding countryside, but scattered irregularly depending on weather conditions. Reports from Soviet and Western scientists indicate that Belarus received about 60 percent of the contamination that fell on the former Soviet Union. But a large area in the Russian Federation south of Bryansk was also contaminated, as were parts of northwestern Ukraine.
Short-Term Impact. Workers involved in the recovery and cleanup after the accident received high doses of radiation. In most cases, these workers were not equipped with individual dosimeters to measure the amount of radiation received, so experts can only estimate their doses. Also, dosimetric procedures varied. Some workers are thought to have better estimated doses than others. According to Soviet estimates, between 300,000 and 600,000 people were involved in the cleanup of the 30-kilometer evacuation zone around the reactor, but many of them entered the zone two years after the accident. (Estimates of the number of "liquidators"--workers brought into the area for accident management and recovery work--vary; the World Health Organization, for example, puts the figure at about 800,000.) In the first year after the accident, the number of cleanup workers in the zone was estimated to be 211,000, and these workers received an estimated average dose of 165 millisievert (16.5 rem).
Some children in the contaminated areas were exposed to high thyroid doses (up to 5,000 rad) because of an intake of radioiodine, a relatively short-lived isotope, from contaminated local milk. Several studies have found that the incidence of thyroid cancer among children in Belarus, Ukraine and Russia has risen sharply (see World Health Organization, page 154; Ivanov, Tsyb Studies, page 159; European Commission Program, page 159; Ukrainian Studies, page 160; and Swiss-Belarussian Paper, page 162). The childhood thyroid cancers that have appeared are of a large and aggressive type, and if detected early, can be treated. Treatment entails surgery followed by iodine-131 therapy for any metastases. To date, such treatment appears to have been successful in all diagnosed cases.
Longer-Term Impact. Right after the accident, the main health concern involved radioiodine, with a half-life of eight days. Today, in addition to radioiodine, there is concern about contamination of the soil with cesium-137, which has a half-life of about 30 years.
According to reports from Soviet scientists at the First International Conference on the Biological and Radiological Aspects of the Chernobyl Accident (September 1990), fallout levels in the 10-kilometer zone around the plant were as high as 130,000 curies per square kilometer. The so-called "red forest" of pine trees killed by heavy radioactive fallout lies within the 10-kilometer zone.
Soviet authorities started evacuating people from the area around Chernobyl within 36 hours of the accident. By May 1986, about a month later, all those living within a 30-kilometer (18-mile) radius of the plant--about 116,000 people--had been relocated.
According to reports from Soviet scientists, 28,000 square kilometers (10,811 sq.mi.) were contaminated by cesium-137 to levels greater than five curies per square kilometer. Roughly 830,000 people lived in this area. About 10,500 square kilometers (4,054 sq.mi.) were contaminated by cesium-137 to levels greater than 15 curies per square kilometer. Of this total, roughly 7,000 sq.km. (2,703 sq.mi.) lie in Belarus, 2,000 sq.km. (772 sq.mi.) in the Russian Federation and 1,500 sq.km. (579 sq.mi.) in Ukraine. About 250,000 people lived in this area. These reported data were corroborated by the International Chernobyl Project.
Several international organizations have studied the environmental and health impacts of the Chernobyl accident. Among them are the World Health Organization and the International Red Cross.
The International Chernobyl Project. The first major assessment of the radiological consequences of the Chernobyl accident, the International Chernobyl Project was led by an advisory group of international experts organized by a number of agencies, including the Commission of the European Communities, the United Nations Scientific Committee on the Effects of Atomic Radiation, the World Health Organization, the Food and Agriculture Organization, the International Labor Organization, and the International Atomic Energy Agency (IAEA).
The international advisory committee was chaired by Dr. Itsuzo Shigematsu, director of the Radiation Effects Research Foundation in Hiroshima, Japan. The IAEA provided the secretariat for the project. More than 200 experts--in medicine, radiopathology, psychology, epidemiology, radioecology, nutrition, dosimetry and radiation protection--were involved.
The experts were divided into teams, which visited the affected areas around Chernobyl many times, performing medical examinations of the local population, gathering data, and taking samples of soil, water, air and food for further analysis.
Because the purpose of the study was to assess the accident's radiological consequences for the people still living in the contaminated areas, it did not include the so-called liquidators. Nor did the project examine what is known as the "forbidden zone" around the damaged reactor.
The report on the project, issued by the IAEA in May 1991, contained conclusions and recommendations with respect to environmental contamination, radiation exposure to the population, health impact and protective measures.
The project experts compared the health of inhabitants from the surveyed contaminated settlements with that of a similar population living in surveyed control settlements where contamination levels are lower but socioeconomic conditions are similar. The teams found significant health disorders in both the contaminated and control settlements, but none was radiation-related.
The experts noted that, as expected, the official Soviet data they examined did not indicate a marked increase in the incidence of leukemia or other cancers. However, several researchers have pointed out that the project's sample size was too small, and the study's time frame too short, to identify an increase in the incidence of tumors with short latent periods, such as leukemia and thyroid cancer. In fact, the project's report noted that "reported absorbed thyroid dose estimates in children are such that there may be a statistically detectable increase in the incidence of thyroid tumours in the future."
World Health Organization. In 1992, a team of medical specialists under the auspices of the World Health Organization's (WHO) regional office in Europe visited Minsk to study reports of an increase in the incidence of thyroid cancer in Belarus. The team examined 11 children in Belarus who had been operated on for thyroid cancer and were hospitalized for treatment or evaluation. The team also studied the histological slides of 104 children who had been diagnosed since January 1989 with thyroid cancer, and examined data on the incidence of thyroid cancer in Belarus.
In a letter on its work published in the British science magazine Nature in September 1992, the team said that the experience in Belarus suggested that the consequences to the human thyroid of radioactive fallout are much greater than previously thought. The team concluded, "The accident and its impact on Belarus poses a challenge to the international community to help...in promoting research for the understanding of the basic processes underlying the phenomenon. Understanding the consequences of Chernobyl will provide an important basis for preventive action in future."
The same issue of Nature carried a letter from medical authorities in Belarus, who reported a "great increase" in cases of thyroid cancer among children, with the greatest increase in the Gomel region, where fallout from Chernobyl was highest. "We believe that the only realistic explanation for the increase...is that it is the direct consequence of the accident at Chernobyl," wrote the authors Vasiliy Kazakov, Yevgeniy Demidchik and Larisa Astakhova.
An October 1992 issue of Nature carried two letters on the subject of childhood thyroid cancer in Belarus. In one, from Valerie Beral and Gillian Reeves of the Cancer Epidemiology Unit, Imperial Cancer Research Fund, Radcliffe Infirmary at Oxford, the authors noted there was "little doubt that the number of children reported to have thyroid cancer increased dramatically in radiation-contaminated areas of the Ukraine in 1990 and in Belarus in 1990-1991."
The authors pointed out that intensive surveillance for thyroid cancer began in these areas in 1990 and many of the cancers might never have been diagnosed otherwise. "More information is needed on the way the thyroid cancers manifested themselves in children from Belarus, on the frequency of thyroid biopsies over time and in different regions, and on the geographical variation in reported thyroid cancer incidence," they wrote. The authors concluded that "an epidemic of thyroid cancer due to radiation exposure would be expected to continue over many years. It will be important to monitor trends in the future. The apparent increase in childhood thyroid cancer in the Ukraine and Belarus is of obvious concern, but it is premature to attribute it entirely to the Chernobyl accident."
In the second letter, I. Shigematsu and J.W. Thiessen of the Radiation Effects Research Foundation in Hiroshima, Japan, said they fully agreed that understanding the consequences of Chernobyl will provide an important basis for preventive action in future. "However, we would add that studies of these consequences must be carefully pursued and based on scientific methodologies. One should not be overly alarmed, nor feel unjustifiably secure, on the basis of evidence that is not definitive."
A November 1992 issue of Nature also carried a letter on childhood thyroid cancer in Belarus. The letter, from Elaine Ron and Jay Lubin of the National Cancer Institute's Epidemiology and Biostatistics Program at the National Institutes of Health, and Arthur B. Schneider of the Division of Endocrinology and Metabolism, Humana and Michael Reese hospitals, University of Illinois, addressed the effect of "better reporting, heightened awareness and screening" on the increase in the number of reported childhood thyroid cancer cases. "To help interpret the Belarus results," wrote the authors, "we estimated the magnitude of the effect of screening in a cohort of children treated at the Michael Reese Hospital by irradiation for benign head and neck diseases."
The authors compared the incidence rates of thyroid cancer among the children before a screening program was begun, during the most active period of screening, and when the level of screening had subsided somewhat. They found the highest incidence rates during the period of most active screening. On the basis of their findings, the authors wrote: "Although our data should not be interpreted as showing that there is no effect of radiation from Chernobyl, they demonstrate that carefully controlled epidemiological studies are needed to understand the true impact of the accident."
In April 1993, on the seventh anniversary of the Chernobyl accident, WHO issued a statement noting that the public health implications of the accident continue to cause great concern, particularly the rise in the number of thyroid cancer cases among children in Belarus.
The International Program on the Health Effects of the Chernobyl Accident (IPHECA), established under the auspices of WHO in 1991, was a cooperative effort involving Belarus, Russia, Ukraine, WHO and several other countries and organizations. The program's aim was to quantify the effects of the Chernobyl accident on the population, provide recommendations for treatment, and devise more effective programs for managing such accidents in the future.
Under the program, five pilot projects were launched: on thyroid disease, hematologic disease, brain damage in utero, management of epidemiological studies, and oral health (in Belarus). The pilot thyroid project, which ran for three years, screened 70,000 children from the contaminated areas of Belarus, Russia and Ukraine to determine the nature of any short-term health effects. The screening identified a very large increase in the incidence of thyroid cancer in the affected countries, according to WHO.
These findings of increased childhood thyroid cancer were reviewed by an international scientific panel and published in a letter in the March 25, 1995, issue of the British Medical Journal. The letter, written by scientists from Belarus, Russia, Ukraine and WHO, reported an increased incidence of childhood thyroid cancer between 1991 and 1994 of 96.4 per million in the Gomel region of Belarus, 11.5 per million in five regions in the north of Ukraine, and 10 per million in Russia's Bryansk and Kaluga regions. The authors concluded: "It is notable that in the regions most affected about 2.3 million children were resident at the time of the accident. This led to unprecedented exposure of a population to ionising radiation, which demands an international response."
These findings, along with those of the other pilot projects, were among the issues discussed at a WHO-sponsored meeting in Geneva in November 1995. The four-day meeting was attended by some 600 scientists, researchers, public health specialists and policymakers from 59 countries. A 38-page summary report of the IPHECA pilot projects and related national programs, Health Consequences of the Chernobyl Accident, was released at that time. The comprehensive 800-page report will be available in March 1996.
Although previously published works in scientific journals had discussed key findings of the studies, the main conclusions were summarized in Health Consequences:
"Psychosocial effects, believed to be unrelated to direct radiation exposure, resulted from the lack of information immediately after the accident, the stress and trauma of compulsory relocation to less contaminated areas, the break in social ties among community members, and the fear that radiation exposure could cause health damage in the future. National registries recorded significant increases in many diseases that are not related to radiation. This is an important health consequence of the Chernobyl accident in view of the size of the population affected and the burden on the health care systems.
"The Chernobyl accident resulted in a sharp increase in thyroid cancer, especially among children living in the contaminated areas. The total number of thyroid cancer cases reported among children (aged 0-14 at the time of diagnosis) in the three countries in the post-accident period was, by the end of 1994, 565 (333 in Belarus, 24 in the Russian Federation, 208 in Ukraine). An increase in childhood thyroid cancer to about 100 times the pre-accident levels was recorded in the Gomel oblast of Belarus which lay in the direct path of the initial cloud of radioactive fallout.
"There was no significant increase in the incidence of leukaemia or other blood disorders. This may be expected given the short time frame of this study. However, since the peak in the incidence of blood disorders may occur more than 10 years after the accident, long-term studies of these diseases are needed.
"Some evidence was found to suggest retarded mental development and deviations in behavioural and emotional reactions in a small group of children exposed to radiation in utero. The extent to which radiation may have contributed to such psychological changes cannot be determined because of the absence of individual dosimetry data.
"The types and distribution of oral diseases observed in the residents of contaminated areas of Belarus were the same as those of the residents of uncontaminated areas."
With the completion of the above project, the International Program on the Health Effects of the Chernobyl Accident was divided into follow-up programs: the International Thyroid Project, which was initiated in Belarus in 1994; accident recovery workers; dose reconstruction; and guidelines on public health action.
The International Thyroid Project is addressing the public health implications of the increase in thyroid disease in children, adolescents and adults. The aim of the project is to provide early diagnosis, improved treatment, and mitigation, where feasible, of childhood thyroid cancer. Activities within the project--not all of which have been fully funded--include:
WHO was also asked to assist health care systems that provide diagnosis, treatment and rehabilitation of the accident cleanup workers--the so-called liquidators--in Russia, Ukraine, and Belarus. That project may also be expanded to include a program that would lay the groundwork for a system to collect data for research.
On dose reconstruction, IPHECA's role would include facilitating international cooperation to encourage use of the best method or methods to achieve accurate retrospective calculations of individual doses.
The project for guidelines on public health actions would assess lessons learned from Chernobyl and identify what emergency actions should be taken in the event of a nuclear accident and the best approaches for investigating the health consequences in populations.
WHO maintains an inventory of ongoing epidemiological work. The 1995 edition of Catalogue of Studies on the Human Health Effects of the Chernobyl Accident includes 84 projects. The inventory consists of three main sections: studies of liquidators, studies of thyroid diseases, and registries.
In addition, WHO has set up a separate project, together with a center in St. Petersburg, Russia, to address the problems of the approximately 800,000 cleanup workers or liquidators.
German, Swiss Projects. From mid-May to early October 1991, staff from the Jülich Research Center in Germany conducted a radioactivity measurement campaign in four regions of Russia to provide information on the radiation exposure of the population in those regions as a result of the Chernobyl accident. The staff first measured environmental and food samples to obtain information on external radiation and on the uptake of radioactivity from the diet, and then examined more than 160,000 people, using whole-body measuring equipment. The staff concluded that "the health of this part of the population was not endangered by food or environmental radioactivity."
In the summer of 1991, a team of Swiss specialists from the Paul Scherrer Institute and Ukrainian specialists carried out approximately 3,400 whole-body and 1,000 food measurements in an area about 50 kilometers (31 miles) west of Chernobyl. The specialists found a wide variation in whole-body dose rates. They concluded that higher doses occurred if Ukrainian authority bans on specific foods were not observed. The specialists also found the highest concentrations of cesium-137 in foods from woodland areas, such as berries, mushrooms and wild animals. The project, which is designed to help the Ukrainian authorities carry out such measurements and to inform and educate the population about radiation, continued in 1992.
In 1994, the nuclear expert committee of VDEW, the German power plant association, launched the GAST-Projekt aimed at providing health care and therapy for sick children in Belarus as well as studying the health impacts of the Chernobyl accident. Project scientists will take biological cell measurements to help predict the development of illness and define optimal treatment. The project will also provide training to doctors in Belarus and supply medicine and medical equipment.
Ivanov, Tsyb Studies. In April 1993, two doctors, Yevgeniy Ivanov and Anatoliy Tsyb, reported the results of their studies of the Chernobyl accident's health effects. Ivanov, director of the Scientific-Technical Research Institute of Hematology & Blood Transfusion of the Belarus Ministry of Health, claimed that his research represented the first attempt at a systematic epidemiological study of the accident's effects on the population of Belarus. He said that his research had failed to produce any evidence of increased incidence of leukemia among the population of Belarus. His research did confirm, however, a rising incidence of thyroid cancer among children, mainly in the Gomel region.
Tsyb, director of the Medical Research Radiological Center of the Russian Academy of Medical Sciences and chairman of the Russian Scientific Commission on Radiological Protection, reported that his study of cleanup workers found a 30-percent increase in diseases in this group, compared with a control group, but these diseases did not include leukemia or other diseases normally associated with radiation exposure.
At an IAEA-sponsored conference on radiation and society in October 1994, Tsyb said there is strong evidence that the increase of thyroid cancer in children in Bryansk, Russia, is the result of irradiation. At the conference, Viktor Ivanov--who works with Tsyb--reported excess mortality of 3 percent per 10 millisievert (1 rem) among the registered Russian liquidators. He said, however, that the causes of death--psychosomatic diseases, suicides--could not be associated with radiation.
European Commission Program. In 1992, the European Commission signed an agreement for international collaboration on the consequences of the Chernobyl accident with representatives of Belarus, Ukraine and the Russian Federation. Under the terms of the agreement, a Coordination Board staffed with representatives from the three countries and the European Union approves projects and participating institutes.
The aim of the projects, which are partnerships between Eastern and Western research institutions and hospitals, is to improve training for scientists in the former Soviet Union, provide financial support to institutes participating in collaborative projects, introduce new technology and train medical specialists, improve the local infrastructure, and create a regional research facility in Belarus, Ukraine and Russia. The European Commission has provided 20 million ECU ($25.2 million) for the program's operation from its inception through 1995, when the collaborative program came to an end, and EC institutes participating in the program have contributed another 5-10 million ECU ($12.6 million).
The EC has suggested that projects studying the health consequences of the Chernobyl accident evaluate them for both the medium term (1-10 years) and long term (10-50 years), evaluate the consequences for the public and the cleanup workers (the "liquidators"), and establish international guidelines for treating victims (e.g., children with thyroid cancer).
Three projects evaluating the health consequences of the accident were launched in 1992: biological dosimetry for people irradiated by the accident; epidemiological investigations, including dose assessment and dose reconstruction; and treatment of accident victims. Three projects were added in 1993: molecular, cellular and biological characterization of childhood thyroid cancer; development of optimal treatment and preventive measures for childhood thyroid cancer; and dose reconstruction and retrospective dosimetry.
In 1992, the European Commission published a report by a panel of experts on childhood thyroid cancer. According to the panel, which documented its findings on the occurrence of childhood thyroid cancer in Belarus and northern Ukraine, there was a true increase in the incidence of this cancer in areas around Chernobyl, and intensive screening programs were unlikely to have accounted for much of the increase. The panel concluded that radioactive iodine was the most likely cause of the increase. The panel also noted that affected children were not receiving optimum treatment, despite the efforts of medical authorities in Belarus and Ukraine, because of the lack of adequate surgical and therapeutic facilities.
In 1994, the European Commission's European Office for Humanitarian Aid launched a project to supply specialist equipment and medicines for the diagnosis, treatment and follow-up of children with thyroid cancer in Belarus and Ukraine.
The work sponsored by the European Commission, as well as by the World Health Organization, is helping to provide a foundation for advances in the capability of Russian, Belarussian and Ukrainian researchers to carry out epidemiological studies of all kinds. This assistance includes training in radiation epidemiology and cancer registration, translation of a book on epidemiology into Russian, and agreement on the development of a common data format between Belarus, Russia and Ukraine. The expertise that Russian, Belarussian and Ukrainian researchers develop is also likely to prove useful in conducting future clinical trials of therapy.
Norwegian Study. In 1994, the Norwegian Radiation Protection Institute released the results of a study of the effects of the Chernobyl accident on Norway's ecosystem. According to the institute, radioactive cesium from the accident could remain in Norway's ecosystem for 10-20 years. Norwegian authorities reportedly estimate that 6-7 percent of the cesium released from Chernobyl came down in Norway.
Ukrainian Studies. Anatoliy Prisyazhiuk of the Ukrainian Scientific Center for Radiation Medicine reported data in 1994--published by the center--on the incidence of childhood leukemia, thyroid cancer and other cancers in three districts within 80 kilometers (50 miles) of the Chernobyl plant. According to the center, data for the period from 1981 to 1993 show a decline in the incidence rate for leukemia in children 10 to 14 years old, but an increase in the incidence rate for thyroid cancer in this age group. The three Ukrainian districts--Polesskoye, Nordichiy and Ovruch--were not evacuated after the accident, but according to soil testing they received the heaviest contamination in Ukraine outside the 30-kilometer (18-mile) zone around the Chernobyl plant.
In a letter published in a June 1995 issue of Nature, Ukrainian and U.K. researchers reported on the increased incidence of childhood thyroid cancer in Ukraine. The authors--Likhtarev, Sobolev and Kairo of the Scientific Center for Radiation Medicine, Tronko, Bogdanova, Oleinic and Epshtein of the Ukrainian Research Institute of Endocrinology and Metabolism, and Beral of the Imperial Cancer Research Fund, Cancer Epidemiology Unit, Radcliffe Infirmary, Oxford--concluded that "the pattern of thyroid cancer in relation to thyroid dose from 131I suggests that the increase in thyroid cancer in childhood reported in the Ukraine is likely to be a direct consequence of the accident at Chernobyl."
French-Russian Study. France's Institute of Nuclear Protection and Safety (IPSN) and the St. Petersburg Center for Ecological Medicine in Russia agreed in October 1994 to conduct a joint study of the so-called liquidators--the civilians and military personnel who participated in the Chernobyl accident cleanup. The two organizations will carry out research in biological dosimetry, which permits an estimation of the dose received by an individual by examining damage to his organism, and in digestive radiobiology, which entails the study of the effects of ionizing radiation on the digestive system.
The official Russian register lists more than 160,000 liquidators, most of whom worked within the 30-kilometer "forbidden zone" in the first two years after the accident and received an estimated average radiation dose of 165 millisievert (16.5 rem).
The St. Petersburg center has a Chernobyl registry with data on about 75,000 liquidators, and is studying about 14,000 of them. Aleksey Nikiforov, director of the center, is reported as saying that the liquidators being treated at the center are ill more often than the general population, suffer from old-age diseases such as arteriosclerosis before the age of 45, and have a much higher incidence of psychological disorders. In addition, the center's doctors are reportedly seeing an increase in solid tumors in the lung, bronchial tubes and stomach.
U.S. Studies. Under an agreement signed between the United States and the U.S.S.R. in 1988, the National Institutes of Health's National Cancer Institute (NCI) has been working with the governments of Belarus and Ukraine to prepare scientific protocols for thyroid studies in those two countries, and for leukemia studies in Ukraine. To support this work, the U.S. government has sent equipment and supplies to Belarus, and plans to send them to Ukraine. NCI is providing scientific, technical and medical expertise to Belarus and Ukraine for all aspects of the studies. In addition, Belarus and Ukraine will provide candidates for professional training in the United States.
The NCI thyroid studies are long-term (10-20 years or more) and involve the evaluation and medical follow-up of about 15,000 people in Belarus and 70,000 people in Ukraine who were children at the time of the Chernobyl accident.
In May 1994, Belarus and the United States agreed on a scientific protocol for the study of thyroid cancer and other thyroid disease among approximately 15,000 children. In July 1995, Ukraine and the United States agreed on a scientific protocol for the study of thyroid disease, especially cancer, among approximately 70,000 children who lived in areas of Ukraine heavily contaminated as a result of the Chernobyl accident. In both countries, children up to 18 years of age, and those in utero, at the time of the accident will be examined for thyroid disease at least every two years. Some 70,000 children had their thyroids measured for radioactivity during the first few weeks following the accident. The studies, which will be funded by the U.S. government, seek to quantify the thyroid cancer risk due to exposure to radioiodine, particularly iodine-131, and the role of potential cofactors, especially dietary iodine deficiency.
The NCI leukemia studies in Ukraine will involve some of the approximately 100,000 Ukrainian clean-up workers ("liquidators") who worked in the Chernobyl area in 1986 and 1987. Using physical and biological dosimetry techniques to reconstruct bone-marrow doses, researchers will study the incidence of leukemia and lymphoma over the next 10-20 years.
In another U.S. study, the Fred Hutchinson Cancer Research Center and the University of Washington, in collaboration with researchers from Russia, will explore the feasibility of physical dose reconstruction and biologic dose estimation; the collection, transportation and storage of blood; and the feasibility of identifying, locating and examining groups of exposed individuals.
Swiss-Belarussian Paper. According to a study published in 1994 by Theodor Abelin of the University of Berne in Switzerland and Belarussian researchers, the incidence of thyroid cancer in children up to 15 years of age in Belarus had risen from less than 0.1 per 100,000 children in 1986 to 2.6 per 100,000 in 1992. The authors' analysis of geographic variation in thyroid cancer in Belarus shows a reasonable correlation with presumptive patterns of radioiodine fallout.
There is no doubt that the Chernobyl accident caused enormous dislocation, stress and anxiety among the people living in the areas touched by the fallout. There is also evidence that it has caused an increase in the incidence of thyroid cancer among children. But radioactive contamination cannot be blamed for all the illnesses reported. Other factors must be considered:
Much of the affected population had never received modern, adequate health care. The extensive medical surveillance given these people since the accident may be uncovering medical problems and conditions that have always existed.
Medical data frequently do not exist for the period before the accident in 1986. As a result, it is difficult to measure the health impact of the Chernobyl accident, because there are often no baseline data to compare with post-accident statistics.
Parts of the affected region--particularly Belarus--are known to be iodine-poor areas with a high incidence of goiters (a thyroid abnormality). As a result, it is not possible to attribute all thyroid-related problems to radioiodine released during the accident.
The latency period for solid cancers--other than leukemia and thyroid cancer--to develop is usually at least 10 years. In spite of lurid reports of thousands of new cancer cases since the accident, there has not been sufficient time to determine the extent of Chernobyl-related cancers. However, several studies have found a sharp increase in the incidence of thyroid cancer among children in contaminated areas of Belarus, Ukraine and Russia. The thyroid cancer latent period is likely to be shorter in children (5-10 years) than in adults (10-15 years).
Medical personnel in the region are generally not well trained in radiation science. Consequently, they attribute many illnesses to radiation, when radiation is not the cause.
There has been an increase--based on historic rates--in cases of high blood pressure, stomach ulcers, anemia and various pulmonary disorders since the accident. Although often attributed to radiation, these illnesses are more likely a result of the tremendous stress imposed on the region's population. Such stress appears to have been exacerbated by scientifically unfounded reports of the health effects of the accident. Also contributing to the rise in stress-related illnesses may be the widespread notion among the affected population that alcohol is an effective antidote to the effects of radiation. Some Western researchers say they have met cleanup workers who believe that death is imminent. This sense of doom, coupled with alcoholism and drug abuse among these workers, may be a factor in the reportedly high suicide rate for this group.
In the longer term, the radiation doses from the accident may lead to an increase in cancers and cancer deaths. The ability to detect future excess cancers, however, will depend on whether groups that received the highest doses and those that received lower doses can be identified and followed up satisfactorily. Unless the mortality registries (and the registries of cancer incidence) and the dose reconstruction exercises are improved substantially, a good correlation between disease and dose is not likely to be achieved.
December 1995
